4 wire system

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petescott

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The question came at work rather or not you have to install yuor neutral wires on the xo from the transformer to your main switch gear on a 480/277 volt y system one master told me no and the other master told me yes but neither one of them could tell were to find the answer in the code book so if any one knows the answer and were to find it in the nec i would like some input thank you
 
Are you asking about the primary or secondary of the transfomer and what voltage is the secondary ?
 
So you're asking if you need to carry the neutral conductor from the transformer secondary XO to the disconnect or panel? Where is the XO to be bonded?
 
petescott said:
The question came at work rather or not you have to install yuor neutral wires on the xo from the transformer to your main switch gear on a 480/277 volt y system one master told me no and the other master told me yes but neither one of them could tell were to find the answer in the code book so if any one knows the answer and were to find it in the nec i would like some input thank you
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Assuming this MDP is not the service, and the system is grounded, but the neutral will not be used as a circuit conductor, IMO no, but a System Bonding Jumper will be needed to connect the EGCs to the Grounded Conductor, sized to 250.66.

If not the service, and the system is ungrounded, then no.

If the neutral will be used as a circuit conductor, then yes.

If the MDP is a service, then yes 250.24(C).
 
wiser folk than myself have changed the way I view this. At one time I thought if you had "XO" on a SDS then it needed to be grounded, but it does appear to me that 250.20(B) only requires that on a 480/277 system when the neutral is used as a circuit conductor.
Not however, that 250.21(C) would require ground fault detectors if you elect to make this an ungrounded system.
 
In this case the mdp would be the main service I believe becuase it is one of the main distribution panels with several secondary panels fed off from it but the question came up because we have no panels useing a neutral so the one master said if we arent useing it then we dont need it and the other one said you still need to put it in
 
See 200.2... The issue has been debated and remains split. I'm on the side that says no grounded conductor necessary if none is used.
 
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